Metallizations comprising nickel oxide

ABSTRACT

In compositions of noble metal(s) dispersed in an inert vehicle which are useful for forming electrodes on dielectric substrates, improved electrode compositions comprising an amount of NiO effective to increase fired conductor adhesion to substrates; since the resultant fired electrodes have increased adhesion to ceramic dielectric substrates, they have special utility in forming surface metallizations in electronic circuits.

[22] Filed:

United States Patent [191 Larry METALLIZATIONS COMPRISING NICKEL OXIDE [75] Inventor: John Robert Larry, Youngstown,

[73] Assignee: E. I. Du Pont de Nemours & Company, Wilmington, Del.

June 5, 1974 [21] Appl. No.: 476,538

Related U.S. Application Data [62] Division of Ser. No. 392,240, Aug. 28, 1973, Pat. No.

[52] U.S. Cl. 427/96; 427/125; 427/126; 427/282; 427/375; 252/514; 252/518; 317/258 [51] Int. Cl. B05D 5/12 [58] Field of Search 117/227; 252/514, 518; 317/258 [56] References Cited UNITED STATES PATENTS 3,207,706 9/1965 Hoffman 252/514 Nov. 25, 1975 3,450,545 6/1969 Ballard et al. ll7/227 X 3,649,567 3/1972 Short ll7/227 X 3,776,769 12/1973 Buck ll7/227 X 3,824,127 7/1974 Conwicke 252/514 X 3,838,07] 9/1974 Amin 252/514 Primary ExaminerMayer Weinblatt [57] ABSTRACT -forming surface metallizations in electronic circuits.

6 Claims, No Drawings 1 METALLIZATIONSI COMPRISING NICKEL oxImz This is a division of application Ser. No. 392,240, filed Aug. 28', 1973-now-U.S. Pat. N01 3,854,957.

BACKGROUND OF THE INVENTION This invention relates to electronic compositions, and more particularly, to metallizations useful in producing high-adhesion conductors on dielectric substrates.

Metallizations which are fired onto ceramic dielectric substrates to produce conductor patterns usually comprise finely divided noble metals and an inorganic binder, and usually are applied to the substrate as a dispersion of the inorganicpowders in an inert liquid medium. The metallic component provides the functional (conductive) utility, while the binder (e.g., glass, Bi O etc.) bonds metal particles to the substrate and to one another. 7

Silver (including Pd/Ag) conductor metallizations (glass frit plus noble metal) presently employed in high-performance electronic applications for producing fired conductor patterns on dielectric substrates are often deficient in that high adhesion (initial and thermally aged) is often not obtained. To prevent adhesive failure, leads to conductor patterns are often designed to impart a mechanical strength which compliments the soldered bond strength. This is done by swagging pins in the ceramic substrate prior to soldering or by using clip-on leads. Better adhesion of the conductor pattern to the substrate would eliminate these steps and result in costs savings. Furthermore, in certain applications, not only is a substrate bearing sintered conductors subjected to a subsequent resistor firing step, but also to an encapsulation fire (glass) at about 500C.; this thermal treatment often leads to poor solderability of conductors located on the substrate.

SUMMARY OF THE INVENTION This invention provides improved powder metallizations comprising noble metals and binder useful for forming conductor patterns on ceramic dielectric substrates. These improved powder compositions are finely divided, in the sense that they can be printed using conventional screen printing techniques, usually as a dispersion in an inert liquid vehicle, in desired patterns on a substrate and then fired (sintered or cured) to form conductors. The conductors have increased adhesion to thesubstrate, both initially (after firing) and after thermal aging.

The improved adhesion is due to the essential and novel additive of the present invention, nickel oxide. The amount of nickel oxide in the powder is an amount effective to increase such adhesion to the substrate, and is 0.ll% by weight, normally in the range O.5l0% by weight, preferably l4%, based on the weight of the noble metal powder present.

Nobel metals are platinum, palladium, gold, silver, ruthenium, and osmium, and mixtures and alloys thereof with one another. Preferred noble metals are platinum, palladium, gold and silver, the optimum noble metal is silver or a mixture of palladium and silver, containing no more than 40% silver.

Also a part of this invention are the resultant fired conductors on dielectric substrates.

DETAILED DESCRIPTION The essential component in the powder compositions of the present invention is finely divided NiO (nickel oxide). The amount employed is sufficient to increase adhesion of the metallization to the substrate upon firing, without severely decreasing the solderability of the resultant fired conductor. Hence, as a practical upper limit, no more than 10% NiO is used, based on the weight of the noble metal present. Preferably about l4% NiO is employed. The minimum amount of NiO employed is that which is effective to increase adhesion of the particular noble metal(s) employed to the substrate; that lower limit in practice is often 0.5% or more.

The compositions of the present invention comprise finely divided inorganic powders dispersed in inert vehicles. The powders are sufficiently finely divided to be used in conventional screen or stencil printing operations, and to facilitate sintering. Generally, the metallizations are such that at least of the particles are no greater than 5 microns. In optimum metallizations substantially all the particles are less than 1 micron in size. Stated another way, the optimum surface area of the particles is greater than about 0.5 mF/g.

The metallizing compositions are prepared from the solids and vehicles by mechanical mixing. The metallizing compositions of the present invention are printed as a film onto ceramic dielectric substrates in the conventional manner. Generally, screen stenciling techniques are preferably employed.

Any inert liquid may be used as the vehicle. Water or any one of various organic liquids, with or without thickening and/or stabilizing agents and/or other common additives, may be used as the vehicle. Exemplary of the organic liquids which can be used are the aliphatic alcohols; esters of such alcohols, for example, the acetates and propionates; terpenes such as pine oil, terpineol and the like; solutions of resins such as the polymethacrylates of lower alcohols, or solutions of ethyl cellulose, in solvents such as pine oil and the monobutyl ether of ethylene glycol monoacetate. The vehicle may contain or be composed of volatile liquids to promote fast setting after application to the substrate. 4

The ratio of inert liquid vehicle to solids in the metallizing compositions of this invention may vary considerably and depends upon the manner in which the dispersion of metallizing composition in vehicle is to be applied and the kind of vehicle used. Generally, from 0.5 to 20 parts by weight of solids per part by weight of vehicle will be used to produce adispersion of the desired consistency. Preferred dispersions contain 30-70% vehicle, and optimum dispersions about 40-60% vehicle.

As indicated above, the metallizing compositions of the present invention are printed onto ceramic substrates, after which the printed substrate is fired to mature (sinter) the metallizing compositions of the present invention, thereby forming continuous conductors on the dielectrics.

The dielectric substrate used in the present invention to make multilayer capacitors may be any dielectric compatible with the electrode composition and firing temperature selected, according to principles well established in the art. Such dielectrics include barium titanate, barium zirconate, lead zirconate, strontium titanate, calcium titanate, calcium zirconate, lead zirconate, lead zirconate titanate, etc. Special advantages as to aged adhesion have been observed where the dielectric is alumina with minor amounts of magnesium silicateand calcium silicate binders.

, As indicated above, the metallizing compositions of a 3 X 3 matrix. The prints were dried, and then fired in a belt furnace in two. firing sequencesgeach with 6-8 minutes at peak temperature; the first sequence was at 850C. and the second at 760C. This simula ted a pro- 'l ).9% PbO, l.22% 3,0,. 9.37% SiO 2.45% CaO, 1.07% AI O, and 75% Bi,O,.

., The respective compositions were each screen A printed on a series. of prefired A1 substrates (which screen having nine 80-mil X 80-mil openings alignedin 55 the present invention are printed onto ceramic subcess involving a conductor fire and a resistor fire, as strates, after which the printed substrate is firedito maoften occurs in hybrid microelectronics fabrication. To' ture the metallizing compositions of the present inventest the adhesion of the tired conductor'tothe subtion, thereby forming continuous conductors. .The strate, wire leads were then attached to the tired conprinted substrate is fired at a temperature below the ductor pads by placing a 20-gauge pretinried copper melting pointof the noble metal used.(to prevent loss Q wireacross three of the firee metallization pads and ofpatterndefinition), at a temperature high enough to then dipping them in a solder pot (62/36/2, Sn/Pb/Ag) mature (sinter) the conductor pattern. For example, at 220C. Bond strengths were then measured by pullwith Pd/Ag conductors firing is. typically, at ing the soldered leads with an ln'stron tester. At least 750- -950?C. for, 5-l0 minutes at peak temperature. nine pads were pulled for each sample to obtain a rep- These dispersions may be printed on any desired diresentative bond strength. Results are reported in the electric substrate; the substrate is normally a prefired Table in the line entitled Initial. A second series of (sintered) alumina ceramic, substrate, although the aged samples were similarly tested (the soldered chip met-allizationcan be printed on-green (unfired) subwith'leads attached were held at 150C. for 48 hours; strates and cofired therewith. results are found in the Table in the line entitled 1 Aged.).

g E A The addition of NiO did not alter the solderability or The following examples and comparative showings solder leach performance of the resultant conductors. are presented to illustrate the advantagesof the present 'Initial and aged adhesionwere each enhanced by NiO invention. In the examples and elsewhere in the specifiadditions. Y

cation and claims, all parts, percentages, proportions, 1 claim: etc., are by weight, unlessotherwise stated. 1. Electrical conductors on a ceramic substrate, the The vehicle used in the examples and showing below conductors consisting essentially of metallizations of wasa screen printing vehicle containing ethyl cellulose finely divided powders comprisingnoble metals and binder dissolved in a solvent of terpineols and dibutyl 0.l10% nickel oxide, by weight of the nobel metal phthalate, plus Baker Castor Oil Co. MFA-6O (sawpresent.

rated long-chain castor oil polymer) flow control agent 2. Electrical conductors according to claim 1 r and soya lecithin wetting agent. wherein the amount of NiO is l-4% I y 3. Electrical conductors according to claim 1 EXAMPLES n .2; 9 Showmg wherein the noble metal is selected from the class con- .The compositions set forth in the Table were presisting of palladium, platinum, gold and silver. pared, printed and firedas follows, to obtain the data 4. Electrical conductors according to claim 1 also set forth in the Table. wherein the noble metal is palladium/silver.

I TABLE- I I Showing A Example 1 Example 2 Paste Components (wt.

Pd(1lm./g.) 1s 18 18 Ag (1.5 m./g.) 45 45 Glass powder 16 16 I6 .NiO. 1 2 Vehicle 21 20 19 Adhesion of Fired Product (p.s.i.):

Initial y 4.5 6.5 6.0 Aged (48 h1-., C.) 2.0 4.4 4.7

5. Electrical conductors according to claim. 2 wherein the noble metal is palladium/silver.

6. Electrical conductors according to claim 3 wherein the noble metal is palladium/silver.

Disclaimer 3,922,387.J0lm Robert Law/y, Youngstown, N.Y. METALLIZATION S COMPRISING NICKEL OXIDE. Patent dated N av. 25, 1975. Disclaimer filed May 26, 1977, by the assignee, E. I. (M Pant (Ze Nemours and Oompany.

Hereby enters this disclaimer to all, claims of said patent.

[Ofioz'al Gazette July 26, 1977.]

Disclaimer 3,922,387.J0hn Robert Larry, Youngstown, NY. METALLIZATION S COMPRISING NICKEL OXIDE. Patent dated N av. 25, 1975. Diselaimer filed May 26, 197 7 by the assignee, E. I. du Pont de Nemmws and Oompemy.

Hereby enters this disclaimer to all claims of said patent.

[Oficial Gazette July 26, 1977.] 

1. ELECTRICAL CONDUCTORS ON A CERAMIC SUBSTRATE, THE CONDUCTORS CONSISTING ESSENTIALLY OF METALLIZATIONS OF FINELY DIVIDED POWDERS COMPRISING NOBLE METALS AND 0.1-10% NICKEL OXIDE, BY WEIGHT OF THE NOBLE METAL PRESENT.
 2. Electrical conductors according to claim 1 wherein the amount of NiO is 1-4%.
 3. Electrical conductors according to claim 1 wherein the noble metal is selected from the class consisting of palladium, platinum, gold and silver.
 4. Electrical conductors according to claim 1 wherein the noble metal is palladium/silver.
 5. Electrical conductors according to claim 2 wherein the noble metal is palladium/silver.
 6. Electrical conductors according to claim 3 wherein the noble metal is palladium/silver. 